
Severus and Lily - Alexandre Desplat
From Harry Potter and the Deathly Hallows pt. 2 OST
I agree with comments I have read on this, it reminds me of Mina/Dracula and Love Remembered, especially around the 40 second mark to around the two minute marker.
These are two gorgeous pieces by Wojciech Kilar that are from Bram Stoker's Dracula (1992). Huge fan of the film, though that aside, I think this music really represents how Severus felt of Lily and continued to feel up until his death.
The sense of innocence at first, the longing, the sadness, the guilt, the hope, the detachment, all of it; the music has a sense of 'eternal', which I like for this. I think you can hear the 'always' coming through. This works for book Severus also I think, not just the movie version imo.